cmd/link: exit early when -d is used on libc platforms

On platforms where we use libc for syscalls, we dynamically link
with libc and therefore dynamic linking cannot be disabled. Exit
early when -d is specified.

Update #42459.

Change-Id: I05abfe111df723b5ee512ceafef734e3804dd0a8
Reviewed-on: https://go-review.googlesource.com/c/go/+/365658
Trust: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>

src/cmd/link/internal/ld/main.go

@@ -172,6 +172,10 @@ func Main(arch *sys.Arch, theArch Arch) {
 		usage()
 	}
 
+	if *FlagD && ctxt.UsesLibc() {
+		Exitf("dynamic linking required on %s; -d flag cannot be used", buildcfg.GOOS)
+	}
+
 	checkStrictDups = *FlagStrictDups
 
 	if !buildcfg.Experiment.RegabiWrappers {

src/cmd/link/internal/ld/target.go

@@ -185,3 +185,13 @@ func (t *Target) mustSetHeadType() {
 func (t *Target) IsBigEndian() bool {
 	return t.Arch.ByteOrder == binary.BigEndian
 }
+
+func (t *Target) UsesLibc() bool {
+	t.mustSetHeadType()
+	switch t.HeadType {
+	case objabi.Haix, objabi.Hdarwin, objabi.Hopenbsd, objabi.Hsolaris, objabi.Hwindows:
+		// platforms where we use libc for syscalls.
+		return true
+	}
+	return false
+}

src/cmd/link/internal/ld/xcoff.go

@@ -1290,10 +1290,6 @@ func Xcoffadddynrel(target *Target, ldr *loader.Loader, syms *ArchSyms, s loader
 }
 
 func (ctxt *Link) doxcoff() {
-	if *FlagD {
-		// All XCOFF files have dynamic symbols because of the syscalls.
-		Exitf("-d is not available on AIX")
-	}
 	ldr := ctxt.loader
 
 	// TOC